Steel vs Aluminum

[Joe45]

I'm going to build a camper box for my HJ45 Land Cruiser long-bed pickup. This will serve as a camper, with a pop-up roof, bed, etc.

I had thought of replacing the bed by building the box over the frame, but the bed is already fitted to the truck and structurally strong, and a full box would require a great deal more engineering and work.



So my thought is to build this so that it fits onto the existing bed, as lightweight as possible.

I have 1.5"x1.5"x1/16" wall square steel tubing that I was thinking of using for the box frame, with 1/16 steel gussets at the corners.

Another option is structural steel studs, which are lighter weight but strong.

Yet another option is aluminum square tubing and angle.

My view is that aluminum, while lighter than steel and relatively strong, is considerably more expensive, requires more specialized equipment to weld, and can be brittle at the welds.
Seems to me that steel, in a 16 gauge or less thickness, can be strong as well as lightweight without losing much to aluminum, and can be easily welded.

Has anyone done any study on this, oir have experience in this subject?

 

[kevgentile]

So, I went through this a while back when building out a sprinter van. I wanted to modularize with steel framing vs standard wood and screw construction, in case I ever need to add, subtract, or repair without having to full demo it.

Steel in general is easier to work with and has a larger margin for error when mig welding. The biggest downside was having to prep and paint all the steel framing when I was done. Remember, hot rolled steel is the most available and affordable, but it has the mill scale that must be removed for a strong weld and optimal paint adhesion. Mill scale is a pain to remove with aluminum oxide strippers, which is what every supply store sells so you'll need to order the proper discs online.

Anyways, 1.5" steel is too big for the main frame and the weight will add up fast. 1.5" .065" wall steel runs 1.26 lbs/ft. Aluminum tube of the same dimensions while less than half the weight, .434 lbs/ft has a lot more deflection than the steel tube, 0.2245" vs steels 0.0756".
You would require an aluminum tube at 1.5" and a wall thickness of 0.250" to match the strength of the thinner steel and it will weigh more to at 1.455 lbs/ft. For my build I used 1" by 0.083" wall steel tube. This netted me 1.00 lbs/ft and a deflection rate of 0.2255", roughly the same as 1.5" aluminum, but yes about twice the weight. Once the 1" tube is boxed in it becomes extremely strong and anything more in size is just waste and weight.
***The deflection numbers are based off of an arbitrary number for the span and center load. They don't necessarily reflect your build but it gives a baseline for the differences in material strength.

You might want to rough out a blueprint and get an idea of the length of material you'll need and get an estimate of the weight you end up with. The other thing to consider is insulation and finish walls. Larger tubing will allow the use of more insulation but as an overland and part-time dweller 1" polyiso is more then sufficient.

 

[Joe45]

So, I went through this a while back when building out a sprinter van. I wanted to modularize with steel framing vs standard wood and screw construction, in case I ever need to add, subtract, or repair without having to full demo it.

Steel in general is easier to work with and has a larger margin for error when mig welding. The biggest downside was having to prep and paint all the steel framing when I was done. Remember, hot rolled steel is the most available and affordable, but it has the mill scale that must be removed for a strong weld and optimal paint adhesion. Mill scale is a pain to remove with aluminum oxide strippers, which is what every supply store sells so you'll need to order the proper discs online.

Anyways, 1.5" steel is too big for the main frame and the weight will add up fast. 1.5" .065" wall steel runs 1.26 lbs/ft. Aluminum tube of the same dimensions while less than half the weight, .434 lbs/ft has a lot more deflection than the steel tube, 0.2245" vs steels 0.0756".
You would require an aluminum tube at 1.5" and a wall thickness of 0.250" to match the strength of the thinner steel and it will weigh more to at 1.455 lbs/ft. For my build I used 1" by 0.083" wall steel tube. This netted me 1.00 lbs/ft and a deflection rate of 0.2255", roughly the same as 1.5" aluminum, but yes about twice the weight. Once the 1" tube is boxed in it becomes extremely strong and anything more in size is just waste and weight.
***The deflection numbers are based off of an arbitrary number for the span and center load. They don't necessarily reflect your build but it gives a baseline for the differences in material strength.

You might want to rough out a blueprint and get an idea of the length of material you'll need and get an estimate of the weight you end up with. The other thing to consider is insulation and finish walls. Larger tubing will allow the use of more insulation but as an overland and part-time dweller 1" polyiso is more then sufficient.

That is very interesting.
Thank you!
I drew up an idea a few weeks back with the thought of using the steel, but the weight is indeed an issue. That's why I thought of structural steel studs; the ones that are I believe 18 gauge or similar. Seems they are pretty strong. But I if the 1"x.083 wall steel tube you are suggesting is better, I can go with that.

Originally I was going to adapt an AluCab Thor roof conversion to the box frame, but decided I can make a camper box for much less and it will suit my build better. I still very much like the AluCab Thor though, absolutely beautiful!

The "walls" of the camper will be rigid insulation foam skinned with "poor man's fiberglass". This is more to avoid the toxic stench and mess of true fiberglass, which I have worked with and absolutely detest.
I will also use gull wing windows to access stuff from outside.

Below is a drawing of the basic frame, and a mock up of how the camper should look. If you notice, in that drawing, I made the camper to look as one with the cab. This would mean replacing the roof with the camper roof, and removing the entire ear window bulkhead, which would make a continuous area like a Troopy-except for still having the lower bulkhead, which I am fine with.
However, I am not sure how I would connect the camper section with the front properly, and whether the flex of the camper will compete with that of the cab.
I do not want to weld on the existing rear window bulkhead, so perhaps buying a beat up one to just use the area that mates up with the doors, or make my own.

If I have to leave the cab as is and make the camper section separate, that is not really a problem though. I will then simply remove the rear window to allow emergency access to the cab, and use a gasket between the cab and the camper.

Please do advise.

Thank you!

 

[kevgentile]

The amount of flex and compatibility really depends on how everything is attached. Fixing the box to the cab roof could pose a problem long term but No way to know until it's too late. I'd probably keep the box/camper section separate, though it'd be super convenient having a full pass-thru.

Here is an lx470 being married to a Sunrader camper box. Might give you some ideas.

 

[Joe45]

That was interesting, thanks.
I asked him about the flex. Let's see if he answers.
The original setup, with the little pickup truck, is kind of the same thing, and no issues with the flex it seems.

I was amazed at the absolutely horrendous materials used in that camper though! Particle board!!! Not even plywood, but particle board! Seems like most RVs are build to look nice but are trash: like frosting on a turd.

 

[cruiserpilot]

However, I am not sure how I would connect the camper section with the front properly, and whether the flex of the camper will compete with that of the cab.

Don't do that. The older FJ45 frame flexes a lot. So unless you physically weld the existing box to the cab keep them separate.
Doing that job of attachment is more involved than just extending sides and bolting it on. Enormous stresses in flex.
I like your idea, aluminum box tube would be my choice, given you can find a good TIG welder, cause that's the best way
to do this.

 

[Joe45]

Don't do that. The older FJ45 frame flexes a lot. So unless you physically weld the existing box to the cab keep them separate.
Doing that job of attachment is more involved than just extending sides and bolting it on. Enormous stresses in flex.
I like your idea, aluminum box tube would be my choice, given you can find a good TIG welder, cause that's the best way
to do this.

Makes sense to keep the box separate then. Thanks. I think What I can do is maybe assemble the aluminum frame using some gussets and rivets, then have it tig welded.

 

[kevgentile]

Makes sense to keep the box separate then. Thanks. I think What I can do is maybe assemble the aluminum frame using some gussets and rivets, then have it tig welded.

over in the sprinter world I saw someone utilize that very same method on a roof rack since he couldn't tig weld. It seemed to do well. I was going to "suggest" this method but figured smaller steel tube and mig would be stronger and require less material.

 

[Joe45]

I found some extrusion, aluminum, that should work. They also make gussets, corner connectors, etc.

 

[kevgentile]

I found some extrusion, aluminum, that should work. They also make gussets, corner connectors, etc.

If you decide to go the extruded route, I'm assuming 80/20? Check with Tnutz.com. I've used them in the past, fair prices.

Only problem with extruded AL is the fasteners can come loose when flexed, and by the time it's all said and done the cost exceeds other options when factoring the extra gussets and hardware.

 

[Joe45]

If you decide to go the extruded route, I'm assuming 80/20? Check with Tnutz.com. I've used them in the past, fair prices.

Only problem with extruded AL is the fasteners can come loose when flexed, and by the time it's all said and done the cost exceeds other options when factoring the extra gussets and hardware.

That's the site I was looking at. Funny.
I'm gonna check the prices etc. once I finalize the design. It may be good part of the build and the other parts use regular aluminum and welding.

 

[Vintij74]

Your ideas are sound, and if you do not have to be limited by height, going over the cab would require about 7 inches of clearance above the cab to allow for the bed box twisting on rough terrain. Troopies bodies do not flex the same way the Longbeds can

As for me, I spent much of 2022, 23 searching for a company who could possible build a bed camper for the FJ45. The only people who are open to building a one-off model is DirtBox out of Colorado. They have a 45 at their shop; possible, though beyond my budget

I chose Gary@mudrak.com to repair multiple broken spotwelds in my pickup bed, after the 2022 Rubithon. I still use a tubular aluminized rack over my bed, and it has been a reliable support for many home lumber projects. after surviving the elements for about 4 years, I replaced the plywood top panels with 2 sheets of 1/8th aluminum (around $280 each) and made the top surface flat, so I could later mount a low profile tent, or solar. I have focused on keeping the great directional visibility of the truck, and so decided that I wanted to just block rain and snow from getting to my gear in the bed. The whole idea of blocking my view of the outdoors and wilderness seems counter to why I have my truck. The pickup bed is vented at the top rails for airflow, if I want to rest thru a storm.
I ‘adopted and re-purposed a stack of 3/8” laboratory polycarbonate shelving, which fit just fine between the tubular uprights, and between the bed and cab. Here is how it handled the May 5th blizzard which stopped traffic in both directions near Truckee. I’m workin on how to enclose the rear, to keep dust and ash out while going thru the icy slush. I run 35’s on springs built to carry the cargo that weighs just about 1700lbs. Had to move the spare out of the bed, so I fabbed a swing out tire carrier. lastly, installing 12V AC with the condenser in the bed (where else can it go?) , powered by a 460A Li Fe Po battery, nearly done after the blizzard shakedown drive. I garage my truck, and so must clear a 7’9” door opening

Your mileage may vary, so good luck with your build!

Rios/Out!

 

[Joe45]

Your ideas are sound, and if you do not have to be limited by height, going over the cab would require about 7 inches of clearance above the cab to allow for the bed box twisting on rough terrain. Troopies bodies do not flex the same way the Longbeds can

As for me, I spent much of 2022, 23 searching for a company who could possible build a bed camper for the FJ45. The only people who are open to building a one-off model is DirtBox out of Colorado. They have a 45 at their shop; possible, though beyond my budget

I chose Gary@mudrak.com to repair multiple broken spotwelds in my pickup bed, after the 2022 Rubithon. I still use a tubular aluminized rack over my bed, and it has been a reliable support for many home lumber projects. after surviving the elements for about 4 years, I replaced the plywood top panels with 2 sheets of 1/8th aluminum (around $280 each) and made the top surface flat, so I could later mount a low profile tent, or solar. I have focused on keeping the great directional visibility of the truck, and so decided that I wanted to just block rain and snow from getting to my gear in the bed. The whole idea of blocking my view of the outdoors and wilderness seems counter to why I have my truck. The pickup bed is vented at the top rails for airflow, if I want to rest thru a storm.
I ‘adopted and re-purposed a stack of 3/8” laboratory polycarbonate shelving, which fit just fine between the tubular uprights, and between the bed and cab. Here is how it handled the May 5th blizzard which stopped traffic in both directions near Truckee. I’m workin on how to enclose the rear, to keep dust and ash out while going thru the icy slush. I run 35’s on springs built to carry the cargo that weighs just about 1700lbs. Had to move the spare out of the bed, so I fabbed a swing out tire carrier. lastly, installing 12V AC with the condenser in the bed (where else can it go?) , powered by a 460A Li Fe Po battery, nearly done after the blizzard shakedown drive. I garage my truck, and so must clear a 7’9” door opening

Your mileage may vary, so good luck with your build!

Rios/Out!

That's a good setup! Thanks for the advice!
7" clearance between the roof and the overhang seems like a lot. Are you sure it would be that much?
If it is, it is, though. I can simply mount the off road lights just ahead of it to cover the gap, at least from a front view. I guess the sides can have the awning mount, etc. that could cover the gap.

Why do the Troopies not flex as much? Is it a stiffer frame, or just the one piece body? I don't think there is any way I could connect the tub or any kind of body to the cab anyway, as the forces twisting the frame will, I am sure, rip it apart. Stiffening the frame I wonder... can that be done? WIll it be detrimental to other parts?
The frame flexing sounds like a positive in some aspects.